Because HDR on PC is a fucking atrocity of nightmares? Honestly, I have a TV that supports HDR10 and Dolby Vision - I plugged my PC into it and started Mass Effect Andromeda and after 2-3 hours I couldn't get either to work.
Was it my nVidia Drivers? Was it the game? Was it the Creators Update for Windows 10? I honestly stopped giving a shit and vowed to not try again until I read enough evidence that someone somewhere had solved the entire thing. I fully expect someone to show up and say "Well yeah you didn't open regedit and modify this key for your specific driver version" - this is why I play games on PS4.
It was Microsoft when they added HDR at the OS level.
Nvidia HDR worked perfect until Microsoft tried to implement it and now its fucked.